For LCD (liquid crystal display), a linear polarizing plate or a circular polarizing plate is employed to control the optical rotation and birefringence in display. For OLED also, a circular polarizing plate is used to prevent reflection of external light.
Heretofore, for such a polarizing plate, an anisotropic dye film obtained in such a manner that iodine or an organic dye having dichromatic properties is dissolved or adsorbed in a polymer material such as a polyvinyl alcohol, and the obtained film is stretched into a film in one direction so that the dichroic dye is oriented, has been widely used (for example, JP-A-3-12606, JP-A-1-160202, JP-A-1-252904) However, a conventional anisotropic dye film produced in such a manner has such problems that the heat resistance or the light fastness may be insufficient depending on the dye or the polymer material used; the yield in bonding of the anisotropic dye film in production of a liquid crystal apparatus tends to be poor. Further, iodine has high sublimation properties and accordingly when it is used for a polarizing plate, the heat resistance and the light fastness are insufficient. Further, the extinction color becomes dark grayish blue, and an ideal achromatic color polarizing plate for the entire visible spectral region can not necessarily obtained.
Accordingly, a method of forming a film containing a dichroic dye on a substrate such as glass or a transparent film by means of a wet film-forming method of coating a solution containing a dichroic dye, and orientating the dichroic dye utilizing e.g. intermolecular interaction to produce an anisotropic dye film has been studied (U.S. Pat. No. 2,400,877, JP-A-8-511109, JP-A-2002-528758, JP-A-2002-180052, JP-A-2002-338838, WO02/099480, and Dreyer, J. F., Phys. And Colloid Chem., 1948, 52, 808, “The Fixing of Molecular Orientation”, Dreyer, J. F., Journal de Physique, 1969, 4, 114, “Light Polarization From Films of Lyotropic Nematic Liquid Crystals”, “Application of Functional Dyes”, supervised by Masahiro Irie, CMC Publishing Co., Ltd., published on Apr. 15, 1996, p. 96-106).
For applications as a polarizing element, in order to obtain higher polarizing performance, an anisotropic dye film having high dichromatic properties has been required, however, such a conventional anisotropic dye film is poor in dichromatic properties, and accordingly no polarizing element excellent in polarizing performance can be obtained.
Heretofore, various dyes have been used for an anisotropic dye film, and selection of the dye is one of important factors. For example, JP-A-3-12606 discloses use of a dichroic dye represented by the following structural formula:

Further, JP-A-1-161202 discloses use of a dichroic dye represented by the following structural formula:

However, the compounds as disclosed in the above JP-A-3-12606 and JP-A-1-161202 have insufficient dichromatic properties, and particular the compound as disclosed in JP-A-3-12606 has a low solubility in various solvents. Accordingly, it can not be said that they are sufficient as a material of an anisotropic dye film to be produced by a wet film-forming method.
Further, JP-A-2002-528758 also discloses use of dichroic dyes represented by the following structural formulae:

However, the above compounds are both disazo compounds, and their dichromatic properties and solubility in a solvent are insufficient as a material of an anisotropic dye film to be produced by a wet film-forming method.
WO02/099480 discloses preparation of an anisotropic dye film to be produced by a wet film-forming method, and discloses, as one example of dichroic dyes to be used, one represented by the following structural formula:

However, the above compound is a disazo compound and has a halogen atom bonded on the triazine ring, whereby it is likely to decompose.